Master information carrier, method for producing the carrier, method and apparatus for writing information into magnetic record medium using the carrier

ABSTRACT

A master information carrier comprises a substrate whose surface has an embossed pattern corresponding to an information signal. At least a surface of the protruding portion of the embossed pattern is made of a ferromagnetic material. A method for writing an information signal into a sheet or disk magnetic record medium with a ferromagnetic thin film or coating is performed by putting the surface of the magnetic record medium into contact with the master information carrier so as to write a magnetized pattern corresponding to the embossed pattern of the master information carrier into the magnetic record medium.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus forrecording information signals into a magnetic record medium used in adevice for magnetic recording and reproduction with high recordingdensity and large capacity, a master information carrier to be used forthe recording method, and a method for making the master informationcarrier.

BACKGROUND OF THE INVENTION

[0002] Recently, a magnetic recording and reproduction apparatus hasbeen increasing recording density to realize small size and largecapacity. Especially, in the field of a hard disk as a typical magneticrecording device, an areal recording density of more than one gigabitper square inch is already available on the market, and an arealrecording density of ten gigabits per square inch is expected in acouple of years. The technology proceeds with a rapid pace.

[0003] One of the primary factors that has enabled such high recordingdensity is the increasing linear recording density, due to improvementsof medium properties, head-disk interface performance, and new signalprocessing method such as “partial response”. However, in recent years,the rate of increase in track density exceeds that of linear recorddensity, and thus becomes a primary factor of the increasing arealrecording density. Practical use of a magneto-resistive type head, whichis superior to a conventional inductive type head in read-back signalperformance, has contributed to the progress in the track density. It ispossible at present to read a signal from a track whose width is only afew microns with good S/N ratio by practical use of themagneto-resistive type head. On the other hand, it is expected that atrack pitch will reach the sub-micron range in the near future alongwith further improvement of the head performance.

[0004] A tracking servo technique is important for the head to read asignal with high S/N ratio by tracing such a narrow track. For example,a conventional hard disk has areas that are located at predeterminedangles over 360 degree and in which information such as a tracking servosignal, address and clock signal are written. In this specification,preformat writing or prewriting of such an information signal is calleda “preformat recording”. A head can trace a track by reading suchinformation in predetermined intervals, and monitoring and correctingthe head position.

[0005] The above mentioned tracking servo signal, address and clocksignal become reference signals for the head to trace a track precisely.Therefore, precise record positions are required for these informationsignals. Current preformat recording into a hard disk is usuallyperformed by magnetic heads placed in the hard disk drive by using aspecial servo track writer after installing the disk and the head intothe drive. In this case, a required accuracy of the track position forwriting is achieved by precisely controlling the position of the headincorporated in the drive by using an external actuator equipped to theservo track writer.

[0006] Such a preformat recording of servo signal, address informationand clock signal is performed similarly for large capacity flexibledisks or disk cartridges, which are removable disk media seen in themarket recently, by using a magnetic head and a servo writer. Thesemedia are removable, so they can be compatibly used by other drives.Therefore, it is not always required to perform the preformat writing bythe heads of each drive after incorporating the heads into the drivethough it is required for a normal hard disk. However, these removabledisks are similar to normal hard disks from the viewpoint that thepreformat writing is performed by precisely controlling the position ofthe head by using an external actuator equipped to the servo trackwriter.

[0007] However, in the present preformat recording of servo signal,address information and clock signal, there are the problems describedbelow.

[0008] The first problem is that writing with the magnetic head is alinear recording relying on relative movement between the magnetic headand the recording medium. This means that a long period is required forpreformat writing by the above-mentioned method, while preciselycontrolling the position of the magnetic head with a servo track writer.Moreover, because the servo writer is expensive, the cost for preformatwriting is high.

[0009] This problem becomes even more serious as the areal recordingdensity increases. This is not only caused by an increase of tracks inradial direction. As the track density increases, a higher precision isrequired for the head positioning and as a result, servo areas, in whichthe tracking servo signal and other signals are recorded, have to beprovided with smaller angular distances between them over 360 degrees.Moreover, the address information to be written as the preformat dataincreases as the recording density increases. Thus more time and costare required for writing more information signals as the record densitybecomes higher.

[0010] A smaller size for magnetic disks is expected to be the trend onthe market. However, large disks of 3.5 or 5 inch size are still indemand. These large disks require more information signals to be writtenfor the preformat than the small disks. The necessary time for preformatwriting influences the cost effectiveness of such large disks.

[0011] The second problem is that a space between the head and a mediumor a diffusive recording magnetic field due to a pole shape of therecord head does not make a steep magnetic transition at track edgeswhere the preformat data is written. Relative movement between themagnetic head and a medium is indispensable in writing with the head, sosome space is necessary between the head and the medium for interfaceperformance between them. A conventional magnetic head usually has twoelements for writing and reading. A pole width at a trailing edge of thehead corresponds to a record track width, and a pole width at a leadingedge is several times larger than that at the trailing edge.

[0012] The above two phenomena may be a factor for causing the diffusiverecording magnetic field to fringe over the preformatted record trackwidth, resulting in the magnetic transition at track edges not beingsteep or erased areas appearing on both sides of a track. In currenttracking servo techniques, the head position is detected by a change inread signal amplitude when the head misses a track. Therefore, as in theprocess of reproducing the data signal recorded between the servotracks, the system requires not only a high S/N ratio of a read signalwhen the head traces a track correctly, but also a steep off-trackperformance, in which the read signal amplitude changes steeply as thehead misses the track. If the magnetic transition is not steep enough atan edge of a track where the preformat is written, it is difficult torealize a precise tracking servo performance that will be required for asubmicron track recording in the future.

[0013] As a solution of the first of the two problems mentioned above, aduplicate record technique of a tracking servo signal or other signalsby using a magnetic transfer technique has been disclosed in JapanesePublication of Unexamined Patent Application (Tokukai) Sho63-183623. Theduplicate record technique of a magnetized pattern using the magnetictransfer technique was originally developed as a method for copying thecontents of a videotape. This technique is explained in detail in C. D.Mee and E. D. Daniel, “Magnetic Recording”, Vol. 3, Chapter 2, p94-105,for example. The method disclosed in Tokukai Sho63-183623 applies theabove duplication technique for videotape to the preformat writing ofthe tracking servo signal or other signals for a flexible disk.

[0014] Such a magnetic transfer technique may improve the productivityof the preformat writing. However, this technique is effective only formedia such as flexible disks that have a small coercive force and a lowareal record density. It is not effective for today's hard disks, whichhave a large coercive force and a high areal record density in the orderof several hundred megabits to gigabit.

[0015] In the magnetic transfer technique, an alternating bias magneticfield has to be applied, whose amplitude is approximately 1.5 times thecoercive force of the target (slave) disk to ensure high transferefficiency. The coercive force of the master disk should be more thanthree times of that of the slave disk, so that the master information,i.e. a magnetized pattern in the master disk, is not erased by thealternating bias magnetic field. Today's high-density hard disk mediahave a coercive force of 120-200 kA/m to enable a high-areal recordingdensity. It is estimated that the coercive force will reach 250-350 kA/mfor an areal record density of 10-gigabit order in the future. Thismeans that a master disk should have a very large coercive force of360-600 kA/m at present and 750-1050 kA/m in the future.

[0016] It is difficult to realize such a large coercive force for amaster disk from the standpoint of a magnetic material. In addition,master information cannot be written into a master disk having such alarge coercive force by any current magnetic recording method.Therefore, considering a possible coercive force for a master disk inthe current magnetic transfer technique, the coercive force of the slavedisk inevitably has an upper limit.

[0017] In the above-mentioned magnetic transfer technique, it ispossible to utilize a thermo-magnetic transfer technique, where insteadof applying the alternating bias magnetic field to the slave disk, theslave disk is heated to the temperature near to the Curie temperaturefor eliminating spontaneous magnetization. However, in that case, theCurie temperature of the slave disk should be much lower than that ofthe master disk. High coercive force magnetic film composed of Co groupmaterials used for a high density magnetic record medium has arelatively high Curie temperature, so it is difficult to realize thecharacteristics required of the master disk and the slave disk for thethermo-magnetic transfer. Therefore, this preformat writing with amagnetic transfer technique cannot be a substantial solution for thebefore-mentioned problems.

[0018] Another solution for these problems is a pre-embossed disktechnique disclosed in Publication of Japanese Unexamined PatentApplication (Tokukai) Hei7-153060 (corresponding to U.S. Pat. No.5,585,989 and European laid open patent application No. 655,734). Inthis technique, an embossed pattern corresponding to a tracking servosignal, address, clock signal and/or other signals is formed on asurface of the disk substrate by a stamper, and a magnetic film isformed on the substrate. This technique can be an effective solution forthe before-mentioned problems. However, the embossed pattern on the disksurface may influence the head's flying float performance (or contactstate in the case of contact writing) when writing or reading, so thatinterface performance between the head and medium may be problematic. Inaddition, the substrate processed by the stamper is usually a polymermaterial (plastic), so it cannot be heated when forming the magneticfilm for ensuring medium properties, and thus a necessary S/N ratiocannot be ensured.

[0019] As mentioned above, a truly effective solution of thebeforementioned two problems, which does not sacrifice other importantperformance such as the medium S/N ratio or the head-medium interface,has not been found yet.

SUMMARY OF THE INVENTION

[0020] Considering the above problems, the present invention provides amethod and apparatus for improving the productivity of the preformatwriting and the sharpness of the magnetic transition at edges of a trackwhere the preformat is written, without sacrificing other importantperformance criteria such as the S/N ratio or the head-medium interface.

[0021] A method for writing a master information signal into a magneticrecord medium according to the present invention uses a masterinformation carrier comprising a substrate; an embossed patterncorresponding to the master information signal formed on the substrate;and a ferromagnetic material that forms at least the surface of theprotruding portion of the embossed pattern. The surface of this masterinformation carrier contacts with a surface of a target magnetic recordmedium having a sheet or disk shape, whose surface has a ferromagneticthin film or coating. Thus, a magnetized pattern corresponding to theembossed pattern on the surface of the master information carrier isrecorded into the magnetic record medium.

[0022] It is preferable that the ferromagnetic material forming thesurface of the protruding portion is a soft magnetic material.Alternatively, it can be a hard or semihard magnetic material whosecoercive force is less than 40 kA/m in the in-plane or perpendiculardirection of the substrate.

[0023] It is more preferable to apply a direct (i.e., not alternating)magnetic field for exciting the ferromagnetic material forming thesurface of the protruding portion, or an alternating magnetic field forassisting the writing of the magnetizing pattern, when the surface ofthe master information carrier contacts with the surface of the magneticrecord medium.

[0024] According to the above-mentioned method of the present invention,a leakage flux is generated from the ferromagnetic material at theprotruding portion of the surface of the master information carrier whenthe ferromagnetic material is magnetized in one direction. This leakageflux performs writing of the magnetized pattern corresponding to theembossed pattern of the master information carrier into the magneticrecord medium. Thus, the preformat writing of the tracking servo signal,address signal, clock signal and other signals is achieved by using theembossed pattern formed on the surface of the master informationcarrier, corresponding to the information signal.

[0025] The writing method of the present invention utilizes a leakagemagnetic field generated from the ferromagnetic material at theprotruding portion due to the change of the magnetic reluctance throughthe embossed pattern. Therefore, the writing mechanism is the same as aconventional magnetic record utilizing a leakage magnetic fieldgenerated from a gap of the magnetic head. However, in the writingmethod of the present invention, the master information of the wholeplane of the master information carrier is written into the magneticrecord medium at one time without relative movement between the masterinformation carrier and the record medium. This characteristic pointdiffers from the writing with magnetic head in the prior art, in whichthe head and the record medium move relative to each other. Thischaracteristic point of the present invention provides an effectivesolution for the previously mentioned two problems, as follows.

[0026] First, the time needed for the preformat writing is substantiallyshort compared with the prior art using a magnetic head. In addition, anexpensive servo-tracking writer is not necessary for precise positioncontrol of the magnetic head. Therefore, the present invention canimprove the productivity of the preformat writing and reduce productioncosts.

[0027] Secondly, a space gap between the master information carrier andthe magnetic record medium can be minimized, since relative movementbetween them is not required for writing the information signal. Inaddition, the leakage magnetic field for writing does not diffuse, whileit diffuses fringing over the record track width in the prior art usinga magnetic head due to a pole shape of the magnetic head. Thus themagnetic transition at edges of a track into which the preformat data iswritten has sharpness compared with the writing with a magnetic head.This ensures a precise tracking of a head in reading data signals fromthe magnetic record medium.

[0028] Furthermore, the method of the present invention does not requirethe limitation of a structure or magnetic performance of the magneticrecord medium in which the master information is written, differentlyfrom the magnetic transfer technique disclosed in Tokukai Sho63-183623or the pre-embossed disk technique disclosed in Tokukai Hei7-153060 aspreviously stated.

[0029] For example, in the magnetic transfer technique disclosed inTokukai Sho63-183623, the master disk requires a substantially highrecord resolution, since the master disk itself is a magnetic recordmedium having master information as a magnetization pattern of themaster disk. Consequently, the magnetic flux density and the filmthickness cannot be enhanced sufficiently for enlarging magnetic fieldintensity for magnetic transfer. In addition, a gradient of the magneticfield for the magnetic transfer becomes small in the magnetic transitionarea since demagnetization occurs due to the repelling poles of thedi-bit. To ensure a sufficient magnetic transfer efficiency with such aweak magnetic field for magnetic transfer, an alternating bias magneticfield is applied, which has an intensity of approximately 1.5 times of acoercive force of the target (slave) record disk. Therefore, thismagnetic transfer technique can be applied only to a flexible disk orother medium with low record density since the coercive force is limitedas previously stated.

[0030] On the contrary, the master information carrier of the presentinvention has the master information as an embossed pattern, and aleakage magnetic field, which is generated from a ferromagnetic materialat a protruding portion of the embossed pattern due to a change of amagnetic reluctance through the embossed pattern, performs the magneticrecording of the master information. The master information carrier doesnot require a high resolution as the magnetic record medium, though itis required for the master disk in the magnetic transfer technique.Therefore a magnetic flux density and a thickness of the ferromagneticmaterial that forms the protruding portion of the surface of the masterinformation carrier can be as large as the magnetic record head used inthe prior art, so that a sharp and large recording magnetic field can beobtained similarly to a magnetic record head. Thus, a sufficient writingability can be obtained for any magnetic record medium, including ausual flexible disk and hard disk and a record medium with a highcoercive force for a gigabit recording in the future.

[0031] The pre-embossed disk technique disclosed in Tokukai Hei7-153060may require a sacrifice of the medium S/N ratio relating to a substratetemperature at film formation process and the head-medium interfaceperformance relating to a head floating performance (or contactingstate), since the substrate material and shape of the disk arerestricted as previously explained. On the contrary, the writing methodof the present invention has no limitation about the substrate materialand surface shape of the disk to be written for the preformat.

[0032] As mentioned above, the writing method of the present inventionprovides an essential solution for the previously mentioned two problemswithout sacrificing other important performances such as the medium S/Nratio and interface performance.

[0033] It is also effective in this writing method to apply analternating and decaying bias magnetic field for obtaining higherwriting efficiency. In this case, there is no possibility of erasing amaster information by the alternating magnetic field or other externalmagnetic field since the master information is formed by the embossingpattern in the master information carrier of the present inventiondifferently from the master information written as a magnetizationpattern in the magnetic transfer technique. Therefore, the coerciveforce of the ferromagnetic material that forms the protruding portion ofthe surface of the master information carrier has no limitation. Theferromagnetic material is not limited to a material with high coerciveforce, but can be selected from a variety of materials such as asemihard magnetic material or a soft magnetic material as long as thematerial can generate sufficient magnetic field for writing the masterinformation into a magnetic record medium.

[0034] In the writing method of the present invention, the ferromagneticmaterial that forms the protruding portion of the surface of the masterinformation carrier should be magnetized in one direction to generate amagnetic field for writing. Therefore, if the semihard or soft magneticmaterial used as the ferromagnetic material cannot generate a stableone-way magnetization, or if a large amplitude of alternating biasmagnetic field is applied, it is necessary to apply a direct excitingfield for exciting the ferromagnetic material and generating an adequateintensity of magnetic field for writing. This direct (not alternating)magnetic field corresponds to the magnetic field generated by a drivecurrent in wiring coils of a magnetic head.

[0035] As mentioned above, the present invention provides a method forpreformat writing of a tracking servo signal, address signal, clocksignal or other signals into a magnetic record medium, especially a diskmedium such as a hard disk or a large capacity flexible disk, withsubstantially high productivity and low cost.

[0036] The present invention also provides more precise tracking for ahigher track density than in the prior art.

[0037] The present invention provides an essential solution for thepreviously stated problems in the prior art without sacrificing anyimportant performances such as a medium S/N ratio or a head-mediuminterface performance. Thus, the present invention will be an importanttechnology for a magnetic record medium with a high record density ofgigabit order and above in the future.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is an enlarged plan view showing an example of a surface ofa master information carrier according to the present invention;

[0039]FIG. 2 shows an example of the master information carrieraccording to the present invention in a cross section along a track;

[0040]FIG. 3 shows another example of the master information carrieraccording to the present invention in a cross section along a track;

[0041]FIG. 4 shows yet another example of the master information carrieraccording to the present invention in a cross section along a track;

[0042]FIG. 5 shows yet another example of the master information carrieraccording to the present invention in a cross section along a track;

[0043]FIG. 6(a) shows a method for writing master information into amagnetic record medium using a master information carrier according tothe present invention;

[0044]FIG. 6(b) shows an example of a record magnetization patternwritten into the magnetic record medium by the method shown in FIG.6(a);

[0045]FIG. 6(c) shows an example of a read signal from the magnetizationpattern written into the magnetic record medium;

[0046]FIG. 7 shows another method for writing master information into amagnetic record medium using a master information carrier according tothe present invention;

[0047]FIG. 8 shows yet another method for writing master informationinto a magnetic record medium using a master information carrieraccording to the present invention;

[0048]FIG. 9(a) shows another method for writing master information intoa magnetic record medium using a master information carrier according tothe present invention;

[0049]FIG. 9(b) shows an example of a magnetization pattern written intothe magnetic record medium;

[0050]FIG. 9(c) shows an example of a read signal from the magnetizationpattern shown in FIG. 9(b);

[0051]FIG. 10 shows an example of a cross section of the protrudingportion of the master information carrier according to the presentinvention along the direction of bit length;

[0052]FIG. 11 shows another example of a cross section of the protrudingportion of the master information carrier according to the presentinvention along the direction of bit length;

[0053]FIG. 12 shows an example of a process for making the masterinformation carrier according to the present invention;

[0054]FIG. 13 shows another example of a process for making the masterinformation carrier according to the present invention;

[0055]FIG. 14 shows yet another example of a process for making themaster information carrier according to the present invention;

[0056]FIG. 15 is a plan view of an example of a master informationcarrier according to the present invention;

[0057]FIG. 16 is a partial cross section showing an apparatus forwriting information signal of the master information carrier shown inFIG. 15 into a magnetic record medium;

[0058]FIG. 17(a) is a perspective view showing a method for writinginformation signal of the master information carrier into a magneticrecord medium using the apparatus shown in FIG. 16;

[0059]FIG. 17(b) is a perspective view showing another method forwriting information signal of the master information carrier into amagnetic record medium using the apparatus shown in FIG. 16;

[0060]FIG. 18 is a perspective view showing an example of a method forpre-magnetizing the magnetic record medium;

[0061]FIG. 19(a) is a plan view of a master information carrieraccording to the present invention;

[0062]FIG. 19(b) show a surface contour of the master informationcarrier shown in FIG. 19(a) along the line C-C′;

[0063]FIG. 20 is a partial cross section showing an apparatus forwriting information signal of the master information carrier shown inFIG. 19 into a magnetic record medium; and

[0064]FIG. 21 is a perspective view showing a method for writinginformation signal of the master information carrier into a magneticrecord medium using the apparatus shown in FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] Below, the preferred embodiments of the present invention areexplained in detail with reference to the accompanying drawings.

[0066] (First Embodiment)

[0067] The following explanation concerns a basic configuration of themaster information carrier according to the present invention and themethod for writing the master information signal into a magnetic recordmedium using the master information carrier.

[0068]FIG. 1 shows an example of a surface of a master informationcarrier according to the present invention. FIG. 1 shows a masterinformation pattern to be written in a preformat area that is disposedat a given predetermined angular distance along circumferentialdirection (i.e. the track direction) for ten tracks in radial direction(i.e. in the direction traversing the track) of the disk. In FIG. 1,areas defined by broken lines correspond to tracks to be used as dataareas in the magnetic record medium after writing the master informationsignal. In a real master information carrier surface, such masterinformation patterns as shown in FIG. 1 are formed at a predeterminedangular distance in circumferential direction and in all tracks over thewhole recording area of the magnetic record disk in radial direction.

[0069] The master information pattern comprises a tracking servo signalarea, a clock signal area and address signal area that are disposedsequentially along the track direction as shown e.g. in FIG. 1. Thesurface of the master information carrier according to the presentinvention has an embossed pattern corresponding to this masterinformation pattern. Each hatched portion in FIG. 1, for example, is aprotruding portion whose surface is made of a ferromagnetic material. Itis preferable to use a ferromagnetic thin film formed by vapordeposition or a plating method as the ferromagnetic material. However, amagnetic coating layer that contains magnetic particles dispersed in anorganic binder, or a bulk material such as sintered material can beused, too.

[0070] The fine embossed pattern corresponding to the information signalas shown in FIG. 1 can be formed easily by utilizing a variety of fineprocessing technique such as a master stamper process for an opticaldisk or a semiconductor process. For example, such a process comprisesthe steps of forming a resist film on a ferromagnetic film, patterningby exposure and development with a photolithography technique or alithography technique using laser or electron beams, and dry etching tomake a fine embossed pattern on the ferromagnetic film. Alternatively,it may comprise the steps of patterning a resist film on a substrate,forming a ferromagnetic film, and removing the resist film to make afine embossed pattern by the ferromagnetic film. This process is calledliftoff method. It is possible to make the fine embossed pattern withoutusing a resist film by a direct fine process using a laser, electronbeam, ion beam, or other machining, as long as the fine embossed patterncorresponding to the information signal is formed with a high precision.Some examples of fine processes that are suited for making the masterinformation carrier of the present invention will be explained in detailunder the Second Embodiment.

[0071] FIGS. 2-4 show examples of a cross section of the masterinformation carrier shown in FIG. 1 along phantom line A-A′. FIGS. 2 and3 show examples whose embossed pattern corresponding to the masterinformation is formed after forming ferromagnetic film 22, 32 on planarsubstrate 21, 31.

[0072] The ferromagnetic film 22 in FIG. 2 remains at the bottom portionas well as the protruding portion of the embossed pattern. On the otherhand, the ferromagnetic film 32 in FIG. 3 remains only at the protrudingportion of the embossed pattern as the bottom portion is in thesubstrate 31. Both examples are acceptable.

[0073] In the example of FIG. 4, ferromagnetic film 42 is formed aftermaking an embossed pattern in the surface of the substrate 41. Thisexample may have a disadvantage in that edges of the surface of theferromagnetic film 42 at the protruding portion have a tendency to beround, so a sharp step may not be obtained. In this case, during thewriting of master information on the magnetic disk medium, the gradientof the magnetic field at a boundary between the protruding portion andthe bottom portion may be decreased and deterioration of writingperformance may occur.

[0074] On the other hand, the configuration of FIG. 2 or 3 is generallypreferable compared with that of FIG. 4 since the magnetic field forwriting may have a sufficiently large gradient at the boundary betweenthe protruding portion and the bottom portion. However, it is necessaryto be careful so that a resist layer or deteriorated layer is completelyremoved from the surface of the ferromagnetic film after making theembossed pattern. Otherwise, the remaining substances may cause spacingloss in the writing process of master information onto the magnetic diskmedium.

[0075] Concerning the material of the substrate, there is no limitationas long as the ferromagnetic film can be formed on the substrate and thefine embossed pattern can be processed precisely corresponding to themaster information signal. However, it is better to use a material whosesurface-roughness is small and which has excellent flatness. If thesurface of the substrate is rough, the surface of the ferromagnetic filmformed on the substrate may be rough too, and a write-spacing loss mayincrease when writing the master information into the magnetic disk. Asa material having a small surface-roughness, a variety of glasses usedfor magnetic disks or optical disks, polymeric material such as apolycarbonate, metals such as Al, Si substrates, or carbon can be used.

[0076] Concerning the above mentioned write-spacing loss, it ispreferable that the surface of the master information carrier and thesurface of the magnetic disk contact with each other securely when themaster information is written into the magnetic disk. Especially if themagnetic record disk into which the master information is written is ahard disk, the surface of the master information carrier preferably isable to compensate a fine wimple or bending of the hard disk to realizea secure contact state over the whole disk surface. Therefore, amaterial having some flexibility, for example a sheet or disk made ofpolymer or thin metal is preferable as the substrate material for themaster information carrier. From this viewpoint, an example of themaster information carrier having a preferred substrate will beexplained later in Third Embodiment.

[0077] A depth of the bottom of the embossed pattern, that is thedistance between the surface of the protruding portion and the bottom,is usually set at more than 0.05 microns, preferably more than 0.1microns, though it depends on the surface condition of the magnetic diskmedium in which the master information is written or the bit size of themaster information. If the ferromagnetic material remains at the bottomof the embossed pattern as shown in FIG. 2 or 4, the depth of the bottombelow 0.1 microns may result in an insufficient gradient of the magneticfield for writing. The depth of the bottom above 0.1 microns ispreferable also for maintaining the secure contact state between thesurface of the master information carrier and the surface of themagnetic disk when the master information is written onto the magneticdisk.

[0078] The ferromagnetic film can be formed by a usual method forforming a thin film, such as sputtering, vacuum vapor deposition,plating, or chemical vapor deposition (CVD).

[0079] A variety of materials can be used for forming the ferromagneticfilm, such as a hard magnetic material, semihard magnetic material orsoft magnetic material as explained previously. However, it is betterthat the saturation magnetic flux density of the material is large togenerate a sufficient magnetic field for writing regardless of a kind ofthe magnetic disk into which the master information is written.Especially, when writing into a disk with a high coercive force above150 kA/m or a flexible disk with a thicker magnetic layer, a materialwith a saturation magnetic flux density above 0.8 T, preferably above1.0 T, is used generally. Otherwise the writing cannot be performedsufficiently.

[0080] Furthermore, the thickness of the ferromagnetic film alsoinfluences the writing ability into the magnetic disk. A certainthickness of the ferromagnetic film is necessary to generate asufficient magnetic field for writing regardless of a kind of themagnetic disk, though, on the other hand, the influence of ademagnetizing field due to the bit shape of the master informationshould be taken into consideration. In the configuration of the presentinvention, the ferromagnetic film of the protruding portion of themaster information disk is magnetized along the track direction in thefilm plane for generating the magnetic field for writing, except for thespecial case where the magnetic disk is a perpendicular magnetic recordmedium or other special cases. However, if the thickness of theferromagnetic film is too large, the writing ability is decreased sincethe leakage flux decreases by the influence of the demagnetizing field.Therefore, the thickness of the ferromagnetic film should be set at anadequate value depending on the bit length of the master information.For example, if the least bit length of the master information is 1-2micron, the adequate thickness of the ferromagnetic film may be 0.1-1.0micron.

[0081] Preferred magnetic characteristics of these ferromagneticmaterials will be explained later together with a method for writing themaster information into the magnetic disk.

[0082]FIG. 5 shows another example of the cross section of the masterinformation carrier along the phantom line A-A′ in FIG. 1. This examplein FIG. 5 differs from the examples shown in FIGS. 2-4 in that thesubstrate itself is made of the ferromagnetic material. In other words,a film formation step is not necessary in this example since theembossed pattern corresponding to the master information is formed onthe surface of the substrate 51 made of the ferromagnetic material.Thus, the productivity for making the master information carrier isimproved compared to FIGS. 2-4.

[0083] If a bulk material such as a sintered material is used for theferromagnetic substrate 51, the surface-roughness of the masterinformation carrier may be large. In this case, the write spacing mayincrease when writing the master information onto the magnetic disk, sothe substrate material chosen should have a surface as smooth aspossible. Generally, a bulk material such as a sintered material doesnot have flexibility, so the example in FIG. 5 is more suitable forwriting into a flexible disk rather than a hard disk.

[0084] A method for writing the master information signal into themagnetic disk using the above-mentioned master information carrier isexplained in the following. FIG. 6(a) shows the method for writing themaster information into the in-plane magnetic record medium. FIG. 6(b)shows a magnetization pattern that was written into the magnetic recordmedium. FIG. 6(c) shows an example of a read-back signal of the abovewritten magnetization pattern detected by a magnetoresistive (MR) typehead. FIGS. 6(a) and 6(b) are both the cross sections of the magneticrecord medium along the track direction.

[0085] When writing onto the in-plane magnetic record medium, theferromagnetic material that forms the protruding portion of the masterinformation carrier 61 is magnetized in the direction 63, along a trackparallel to the surface of the magnetic record medium 62, as shown inFIG. 6A. This magnetization 63 is given by residual magnetizationgenerated by previously saturating the ferromagnetic material that formsthe protruding portion along the track direction, e.g. if theferromagnetic material of the protruding portions is a highly coercivematerial. Materials composed of rare earth elements and transition metalmaterial such as Sm—Co or Ne—Fe—B are suitable as highly coercivematerial for the above mentioned ferromagnetic material since they havea high coercive force and high saturation flux density.

[0086] The surface of the master information carrier 61 causes a changeof the magnetic reluctance due to the embossed pattern. Thus, themagnetization 63 of the ferromagnetic material at the protruding portiongenerates the magnetic field 64 for writing. This magnetic field 64 hasopposite polarities for the surfaces of the protruding portion and thebottom of the master information carrier 61. Consequently, themagnetization pattern 65 shown in FIG. 6(b) is written into the magneticrecord medium 62, corresponding to the embossed pattern.

[0087] The read signal waveform is shown in FIG. 6(c), which is readusing a magnetic head and attained from the magnetization 65 recorded bythe method of the present invention. The waveform shown in FIG. 6(c) isbasically similar to that of the signal read from the magnetizationrecorded by the method in the prior art using a magnetic head.Therefore, there is no problem in processing the read signal. Thewriting method of the present invention is rather superior regarding thesymmetry of the read signal to the method using a magnetic head,probably because the method of the present invention is not accompaniedby relative movement of the master information carrier and the magneticrecord medium.

[0088] In the writing step according to the present invention, applyingan alternating and decaying bias magnetic field improves the efficiencyof writing, as explained before. Considering the technical field of theinvention, it is preferable to utilize a basically digital saturationrecording in the writing process of the present invention. However,there may be some cases with insufficient writing ability depending onthe information signal pattern to be written or the magneticcharacteristics of the magnetic record medium. In these cases, applyingthe alternating and decaying bias magnetic field will be effective meansto obtain a sufficient saturation writing.

[0089] A writing mechanism with applying the alternating bias magneticfield is basically the same as an analog alternating bias writing in theprior art. However, the recording method of the present invention is astatic recording without relative movement between the masterinformation carrier and the magnetic recording medium. Therefore, afrequency of the alternating bias magnetic field is not as limited asthe analog alternating bias writing in the prior art. The frequency ofthe alternating magnetic field to be applied in the method of thepresent invention can be 50 or 60 Hz, as is used for commercial AC powersupply.

[0090] A decay time of the alternating bias magnetic field is setsubstantially longer than a period of the alternating bias magneticfield, preferably more than five periods. For example, if the frequencyof the alternating bias magnetic field is 50 or 60 Hz, more than 100 msmay be enough for the decay time.

[0091] On the other hand, the method shown in FIG. 6(a) requires amaximum amplitude of the alternating magnetic field that is less than acoercive force of the ferromagnetic material that forms the protrudingportion of the master information carrier 61. In the method shown inFIG. 6(a), applying an alternating bias magnetic field greater than thecoercive force of the ferromagnetic material will decrease themagnetization 63 of the magnetic material of the protruding portion. Inthis case, it is difficult to obtain a sufficient magnetic field 64 forwriting.

[0092] In the above explanation, a highly coercive material is used forthe ferromagnetic material that forms the protruding portion of themaster information carrier. However, there are some cases where it isdifficult to get a sufficient magnetization with an easy magnetizationdirection set along a track, owing to the embossed pattern formed on thesurface of the master information carrier when using a highly coercivematerial.

[0093] For example, if a bit shape of the master information signal iselongated in the direction across the tracks, the ferromagnetic materialthat forms the protruding portion of the master information carrier isinfluenced by shape anisotropy in the direction across tracks so thatthe direction across the tracks tends to be an easy axis. In this case,the residual magnetization generated by saturating the ferromagneticmaterial along the track is too small to obtain a magnetic field alongthe track for writing. In addition, a hard magnetic highly coercivematerial usually has difficulty in controlling magnetic anisotropy.Therefore, it is difficult to induce the anisotropy that is enough tocompensate the contribution of the above mentioned bit shape, in thedirection along the track.

[0094] To solve the above-mentioned problem, it is preferable to makethe ferromagnetic material that forms the protruding portion of themaster information carrier using a soft magnetic material or a hard orsemihard magnetic material having lower coercive force. There is nospecific boundary between a hard magnetic material and a semihardmagnetic material. In this specification, the term “semihard magneticmaterial” is used as a generic term for hard or semihard magneticmaterials having a small coercive force (below 60 kA/m for example),that is less than a half value of a usual magnetic record medium(120-200 kA/m).

[0095] Such a soft or semihard magnetic material can be treated easilyto have an adequate anisotropy by adding a variety of energies in theprocess of making the material or annealing the material in the magneticfield, compared with a hard magnetic material having a highly coerciveforce. Therefore, the above mentioned anisotropy due to the bit shapemay be compensated easily, too. Furthermore, many soft or semihardmaterials have a large saturation flux density suitable for theferromagnetic material that forms the protruding portion of the masterinformation carrier. As the soft magnetic material suitable for theferromagnetic material that forms the protruding portion of the masterinformation carrier of the present invention there are, for example, acrystalline material such as Ni—Fe or Fe—Al—Si, an amorphous material ofthe Co group such as Co—Zr—Nb, or an Fe microcrystalline material suchas Fe—Ta—N. For the semihard magnetic material having a low coerciveforce, for example, Fe, Co, Fe—Co and other materials are suitable.

[0096] Though the ferromagnetic material that forms the protrudingportion of the master information carrier in the present inventionshould be magnetized in one direction to generate a magnetic field forwriting in a writing process, a soft magnetic material or a semihardmagnetic material usually does not provide a stable one-directionmagnetization in a residual magnetization state. Therefore, in manycases, a direct exciting field is applied for exciting the material togenerate an adequate magnetic field for writing. As mentioned before,this direct exciting field corresponds to a magnetic field generated bya current that flows in coil windings of the magnetic head.

[0097]FIG. 7 shows the method for writing the master information signalusing a direct magnetizing field as mentioned above. FIG. 7 is also thecross section along the track of the magnetic record medium similar toFIG. 6(a).

[0098] The soft magnetic material or the semihard magnetic material thatforms the protruding portion of the master information carrier ismagnetized by the direct exciting field 75 in the direction along thetrack of the magnetic record medium 72 to generate the magnetic writefield 74. The direct exciting field 75 cannot be so strong since it isapplied to the magnetic record medium 72, too. The intensity of thedirect exciting field 75 is preferably as large as, or below thecoercive force of the magnetic record medium in most cases. If theintensity of the direct exciting field 75 is as large as, or less thanthe coercive force of the magnetic record medium, the magnetic field forwriting 74 generated by the soft magnetic material or the semihardmagnetic material of the protruding portion is much stronger than theintensity of the direct exciting field. Thus, the magnetization patterncan be written corresponding to the embossed pattern, in the same manneras shown in FIG. 6(b). The adequate intensity of the direct excitingfield 75 can be varied due to the magnetic characteristics of the softor semihard magnetic material that forms the protruding portion of themaster information carrier, magnetic characteristics of the magneticrecord medium, embossed pattern shape, or other factors. Therefore, theintensity of the direct exciting field should be optimizedexperimentally to obtain the most adequate writing characteristics ineach case.

[0099] From the above viewpoint, the soft or semihard magnetic materialthat forms the protruding portion of the master information carrierpreferably reaches substantial saturation by the direct exciting field75 whose intensity is as large as, or below the coercive force of themagnetic record medium. Most soft magnetic materials show goodsaturation characteristics in a small magnetic field. However, somesemihard magnetic materials need a large magnetic field for saturation,so attention should be paid when selecting the material. Material havinga coercive force below 40 kA/m is preferable as the semihard magneticmaterial when writing into a hard disk having a usual coercive force ora large-capacity flexible disk. If the coercive force is more than 40kA/m, an intensity of the direct exciting field 75 that is significantlylarger than the coercive force of the magnetic record medium isnecessary for stable magnetization of the semihard magnetic materialalong the track of the magnetic record medium 72. Thus, it is difficultto write with a precise resolution in some cases.

[0100] The writing method with applying the direct exciting field asshown in FIG. 7 is effective also in the case where the ferromagneticmaterial that forms the protruding portion of the master informationcarrier has a large coercive force, especially when applying analternating bias magnetic field whose intensity is larger than thecoercive force. As mentioned above, if an alternating bias magneticfield that is larger than the coercive force of the ferromagneticmaterial is applied in FIG. 6, the magnetization 63 of the ferromagneticmaterial that forms the protruding portion decreases, so that asufficient magnetic field for writing 64 cannot be obtained. In thiscase, by superposing the direct exciting field on the alternating biasmagnetic field, the total external magnetic field that is applied in theopposite direction to magnetization 63 of the ferromagnetic materialdecreases, so that the stable magnetic field for writing can begenerated similarly to the case where the alternating bias magneticfield is not applied. Application of the alternating and decaying biasmagnetic field superposed on the direct exciting field as mentionedabove is also effective for the case where the ferromagnetic materialthat forms the protruding portion of the master information carrier is asemihard or soft magnetic material.

[0101] In some cases depending on the embossed pattern on the surface ofthe master information carrier, a better written state can be obtainedby erasing the magnetic record medium previously with a directsaturation and giving an initial magnetization 86 in one direction asshown in FIG. 8.

[0102] The embossed pattern can be a variety of patterns depending onthe information signal required for each application. Therefore, in someembossed pattern, either the magnetic field on the surface of theprotruding portion site or the magnetic field on the bottom portion siteis much weaker than the other. Thus, the weaker magnetic field cannotperform saturation writing, or the linearity of writing is deteriorated.In FIG. 8, it is preferable to erase the magnetic record medium 82previously by a direct saturation in the direction of the weakermagnetic field, which is either the magnetic field 84 a on the surfaceof the protruding portion site or the magnetic field 84 b on the bottomportion site, to promote the saturation writing in this direction.

[0103] In FIG. 8, the magnetic record medium 82 is previously erasedwith the direct saturation magnetization in the opposite direction tothe magnetization 83 of the ferromagnetic material that forms theprotruding portion. However, it is clear from the above explanation thatthe polarity for erasing a magnetic record medium by the directsaturation depends on the case. For example, in some cases, a betterresolution for writing is obtained by erasing the magnetic record medium82 using a direct saturation in the same direction as the magnetization83 of the ferromagnetic material at the protruding portion of the masterinformation. Though the direct exciting field 85 is applied in theconfiguration shown in FIG. 8 in the same manner as shown in FIG. 7, theeffect of previously erasing with a direct exciting field is obtainedeven if the direct exciting field 85 is not applied.

[0104] The above explanation concerns writing into in-plane magneticrecord media. However, the writing method of this invention can beutilized for various magnetic recording media in a variety ofembodiments to obtain similar effects.

[0105] A typical variation of the writing method according to thepresent invention is shown in FIG. 9 where the master information iswritten into a perpendicular magnetic record medium. FIG. 9(a) shows thewriting method of the master information signal into the perpendicularmagnetic record medium using a master information carrier. FIG. 9(b)shows a magnetization pattern written into the perpendicular magneticrecord medium. FIG. 9(c) shows an example of the waveform of a readsignal read by a magnetoresistive (MR) type head from the magnetizationpattern. FIGS. 9(a) and 9(b) are cross sections along the trackdirection of the magnetic record medium similar to FIGS. 6-8.

[0106] When writing into the perpendicular magnetic medium,magnetization 93 is applied to the ferromagnetic material of theprotruding portion of the master information carrier 91 in the directionperpendicular to the surface of the magnetic record medium 92.Therefore, if the ferromagnetic material of the protruding portion is aferromagnetic film, a thickness of the film should be large enough forreducing a demagnetization field in the direction perpendicular to thesurface.

[0107] If the direct exciting field 95 is applied, its direction shouldbe perpendicular to the surface of the magnetic record medium 92,differently from the in-plane writing. The previous erasing of themagnetic record medium 92 with direct saturation is performed also inthe direction perpendicular to the surface of the magnetic record medium92 so that the initial magnetization 96 can remain in the verticaldirection.

[0108] (Second Embodiment)

[0109] This second embodiment will explain an example of the masterinformation carrier having superior record resolution uniformly over thelarge area, and an example of the process for making the masterinformation carrier efficiently at a low cost.

[0110] In the above mentioned first embodiment, the surface of themaster information carrier shown in FIGS. 1-5 should be processed tomake a fine embossed pattern corresponding to the information signal tobe written for preformat, using photolithography or other techniques.However, depending on the process for making the master informationcarrier, it is sometimes difficult to form an embossed patterncorresponding to the information signal with a sufficient resolution,when forming the embossed pattern with a high record density in which abit length is below several microns. Especially, if the masterinformation disk is to be used for writing into a disk with largediameter such as 3.5 or 5 inches, usual photolithography process cannotprovide a uniform accuracy over such a large area, so the embossedpattern may have some microscopic difference depending on its location.

[0111] For example, the master information carrier having a crosssection shown in FIG. 3 was made by steps of forming a ferromagneticfilm 32 on the surface of the planar substrate 31, coating a resist filmon the surface, exposing and developing the resist film to form thepattern corresponding to the digital information signal, and forming thefine embossed pattern on the surface of the ferromagnetic film by a dryetching technique such as an ion milling.

[0112] Though the section profile of the protruding portion issimplified with a rectangular shape in FIG. 3, it is difficult to formsuch a rectangular section over a large area in a real masterinformation carrier made using regular photolithography. The sectionprofile of the protruding portion usually assumes a trapezoidal shape,where the length of the upper side differs from the length of the lowerside, not a rectangular shape. In addition, the edges of the upper sideat the surface of the trapezoid become rounded in general.

[0113] Such a section profile results primarily from the fact that theresolution of the exposing or developing process of the resist film isnot sufficient for the bit length of the digital information signal. Thesection profile of the patterned resist film has already been atrapezoid and its edges at the upper side have already been rounded.Thus, the section profile of the protruding portion of the ferromagneticfilm that is formed by the dry etching technique such as the ion millingbecomes a rounded trapezoid, inheriting the section profile of thepatterned resist film.

[0114] Furthermore, the above mentioned section profile cannot beuniform over a large area, so some microscopic differences of thesection profile may be observed depending on the location, in spite ofhaving the same patterning. Such a microscopic difference of the sectionprofile of the embossed pattern may undesirably influence the S/N ratioof the signal written for the preformat.

[0115] The above problem can be solved by using an advancedphotolithography technique that can realize sufficient accuracy andresolution over the large area. However, in this case, even if the aboveproblems are solved, a substantially expensive exposing machine, resistmaterial, developing liquid and other things are necessary.Consequently, the productivity of the master information carrier maydrop and the cost for making the master information carrier may rise.

[0116] On the contrary, this embodiment can control the variation of theS/N ratio due to the variation of the section profile within a certaintolerance by improving the section profile of the embossed pattern evenif an inexpensive photolithography process is used.

[0117] The inventors have searched for a preferred section profile ofthe embossed pattern that has little influence on the S/N ratio of thesignal. As a result, it was found that a first or second configurationof the protruding portion of the master information carrier explainedbelow can control the variation of the S/N ratio within a certaintolerance.

[0118]FIG. 10 shows a first configuration of the protruding portion. Inthis configuration, the section profile of the protruding portion alongthe bit length direction of the digital information signal issubstantially a trapezoid with an upper side at the surface and a lowerside on the substrate. The upper side length “a” is less than the lowerside length “b”, and the difference (b−a) between the both side lengthsis less than twice the height of the trapezoid. Such a section profileof the protruding portion can control the variation of the S/N ratio dueto the microscopic variation of the section profile within a certaintolerance, even when writing a digital information signal for thepreformat, with several microns bit-length.

[0119] The S/N ratio of the read signal is influenced not only by theintensity of the magnetic field for preformat writing generated from theferromagnetic film 102 at the protruding portion of the masterinformation carrier, but also the gradient of the magnetic field at theboundary between the protruding portion and the bottom, i.e., at theedges of the upper side of the protruding portion. If the differencebetween the upper side length “a” and the lower side length “b” of thetrapezoid section of the protruding portion is less than twice of theheight “h” of the trapezoid, the gradient of the magnetic field israther steep. Therefore, it could be established that the S/N ratio ofthe read signal is large and the variation of the S/N ratio due to themicroscopic variation of the section profile is small under the abovecondition.

[0120] On the contrary, if the difference between the upper side length“a” and the lower side length “b” is more than twice of the height “h”of the trapezoid, leakage from slant faces decreases the gradient of themagnetic field at the edges of the upper side. Therefore, the variationof the S/N ratio of the read signal due to the variation of the sectionprofile increases beyond a certain tolerance, so that a uniform andsufficient S/N ratio of the read signal cannot be obtained over a largearea.

[0121] If the bit length of the digital information signal to be writtenis less than one micron, field gradient variation due to the microscopicshape variation at the edges of the upper side can influence the S/Nratio of the read signal. In this case, curvature radii r, r′ at edgesof the upper side are preferably set below a half of the upper sidelength. Thus, the variation of the S/N ratio due to the microscopicvariation of the section profile is controlled within a tolerance, evenwhen a digital signal with a bit length of less than 1 μm is recorded.

[0122] As mentioned above, the first configuration permits the sectionprofile of the protruding portion to have a trapezoid shape, so theembossed pattern can be formed by a regular, widely usedphotolithography process, without having to use an advancedphotolithography technique. Therefore, the master information carrierhaving the first configuration can be produced efficiently at low cost.

[0123] As explained in the first embodiment, the thickness of theferromagnetic film may influence the S/N ratio of the read signal whenperforming preformat writing by use of the above mentioned masterinformation carrier. If the thickness of the ferromagnetic film 102 inFIG. 10 is too thin, a sufficient magnetic field cannot be generated forwriting, and the gradient of the magnetic field may decrease at theboundary of the protruding portion and the bottom portion. Thus, it isdifficult to perform sufficient writing.

[0124] On the other hand, when writing a preformat signal into anin-plane magnetic record medium, if the thickness of the ferromagneticfilm 102 is too thick, the demagnetizing field due to the profile of theprotruding portion makes it difficult to generate a sufficient magneticfield. For example, preformat writing into the in-plane magnetic disk isperformed by applying a direct exciting field along the circumferentialdirection in the disk plane for magnetizing the ferromagnetic film 102at the protruding portion of the master information carrier, and thedigital information signal corresponding to the embossed pattern iswritten. However, if the upper side length “a” of the protruding portioncorresponding to the bit length of the signal is not sufficiently largerthan the thickness of the ferromagnetic film 102, the demagnetizingfield in the opposite direction to the magnetization of theferromagnetic film 102 increases, so that the magnetic field for writinggenerated by the protruding portion is weakened.

[0125] The influence of the above mentioned demagnetizing field causes adrop of the S/N ratio if the thickness of the ferromagnetic film 102 islarger than a half of the upper side length “a” of the protrudingportion. However, the drop of the S/N ratio is small enough to beneglected if the thickness of the ferromagnetic film 102 is smaller thana half of the upper side length “a” of the protruding portion.Therefore, it is preferable to ensure that the thickness of theferromagnetic film 102 can generate a sufficient magnetic field forwriting in a thickness region below one half of the upper side length“a”, especially in a master information carrier with in-plane preformatwriting.

[0126] On the other hand, when writing the preformat signal into aperpendicular magnetic record medium, a direct exciting field is appliedin the direction perpendicular to the ferromagnetic film 102 tomagnetize the ferromagnetic film 102, and a digital information signalis written corresponding to the embossed pattern. In this case,differently from the case with in-plane writing, the magnetic field forwriting is dropped due to the demagnetizing field, the more theferromagnetic film becomes thinner. Therefore, a master informationcarrier to be used for preformat writing into the perpendicular magneticrecord medium should have a thickness of the ferromagnetic film 102 thatis larger than the upper side length “a”, preferably more than twice theupper side length “a” of the protruding portion of the ferromagneticfilm 102.

[0127]FIG. 11 shows a second configuration of the protruding portion. Inthis configuration, the section profile of the protruding portion alongthe direction of the bit length of the digital information signal issubstantially a trapezoid with an upper side at the surface and a lowerside on the substrate, and the upper side length “a” is larger than thelower side length “b”. This upside-down trapezoid section of theprotruding portion can obtain a sufficient S/N ratio of the read signaland control the variation of the S/N ratio within a tolerance over alarge area, in spite of some microscopic variation of the sectionprofile, even when a digital signal with a bit length of less than 1 μmis recorded.

[0128] As previously mentioned, the S/N ratio of the read signal isinfluenced by the intensity of the magnetic field for preformat writinggenerated from the ferromagnetic film at the protruding portion of themaster information carrier, and by the gradient of the magnetic field atthe boundary between the protruding portion and the bottom portion, thatis the edges of the upper side of the protruding portion. In the secondconfiguration, the angles between the upper side and slant faces areacute angles since the upper side length “a” is larger than the lowerside length “b” of the trapezoid section of the protruding portion. Sucha configuration reduces the influence of the leakage magnetic fieldgenerated by the slant faces and provides a steep gradient of themagnetic field at the edges of the upper side, so that a sufficient S/Nratio of the read signal is obtained.

[0129] Furthermore, the difference between the upper side length “a” andthe lower side length “b” as well as the gradient variation of themagnetic field at each edge of the upper side is small in the secondconfiguration. As a result, the variation of the S/N ratio of the readsignal due to the microscopic variation of the section profile also canbe within a tolerance. Therefore, as in the first embodiment, a uniformand sufficient S/N ratio of the read signal over a large area can beobtained.

[0130] The thickness of the ferromagnetic film 112 influences the S/Nratio of the read signal in the second configuration, too. The standardfor determining the thickness of the ferromagnetic film 112 is the sameas that mentioned in the first configuration. The thickness of theferromagnetic film 112 is preferably less than a half of the upper sidelength “a” for the master information carrier for an in-plane magneticrecord medium, and is preferably more than twice the upper side length“a” for the master information carrier for a perpendicular magneticrecord medium.

[0131] The master information carrier having the second configurationcan be manufactured by a photolithography technique using, for example,a liftoff process. The following explains an example of a processsuitable for making a master information carrier having the secondconfiguration.

[0132]FIG. 12 shows an example of the process for making the masterinformation carrier according to the second configuration.

[0133] First, as shown FIG. 12(a), the embossed pattern corresponding tothe digital information signal is formed on the substrate 121 with thephotoresist film 123. The cross section in the bit-length direction ofthe protruding portion formed by the photoresist film 123 issubstantially trapezoidal with an upper side at the surface and a lowerside on the substrate, and the upper side length is shorter than thelower side, as shown in FIG. 12(a).

[0134] Then, as shown in FIG. 12(b), the ferromagnetic film 122 isformed on the substrate 121 and the protruding portion formed by thephotoresist film 123. A usual method such as a vacuum vapor deposition,sputtering or plating can be used for forming the ferromagnetic film122.

[0135] Then, as shown in FIG. 12(c), the surface of the ferromagneticfilm 122 is etched a little by ion milling or another method. Afterthat, the photoresist film 123 and the ferromagnetic film 122 formed onthe photoresist film 123 are removed by a liftoff method. Thus, as shownin FIG. 12(d), the master information carrier is made, which includesthe substrate 121 and the protruding portion of the ferromagnetic film122 formed on the substrate 121, and the section profile of theprotruding portion is a trapezoid with an upper side longer than a lowerside. The liftoff process is performed by melting the photoresist film123 by using a special solvent called “remover”, for removing theferromagnetic film 122 formed on the photoresist film 123 together withthe photoresist film 123.

[0136] The etching step of the ferromagnetic film surface shown in FIG.12(c) is performed for making the liftoff easy by removing theferromagnetic film 122 deposited on the slant faces of the protrudingportion formed with the photoresist film. This step can be eliminated ifthe thickness of the ferromagnetic film 122 is thin. In this case,however, the accuracy of patterning of the ferromagnetic film 122 afterthe liftoff may be deteriorated and ferromagnetic film or photoresistfilm 123 can remain partially. Therefore, it is better not to eliminatethe etching step shown in FIG. 12(c).

[0137] In the etching step shown in FIG. 12(c), ion milling for etchingthe ferromagnetic film can be replaced with a vacuum dry process such assputter etching or a wet process such as chemical etching.

[0138] If a vacuum dry process such as sputtering or ion milling is usedfor this etching step, it is preferable to irradiate the ion 124 fromthe slant direction against the surface of the substrate 121 since thisetching process is performed for making the liftoff easy by removing theferromagnetic film 122 deposited on the slant faces of the protrudingportion formed with the photoresist film 123. According to experiments,it was found that the ferromagnetic film 122 deposited on the slantfaces can be removed effectively when an incident angle of the ion 124with respect to the normal of the substrate 121 is more than 20 degrees.

[0139]FIG. 13 shows another example of the process for making the masterinformation carrier having the second configuration.

[0140] First, as shown in FIG. 13(a), a conductive film 134 is formed onthe substrate 131. Then, an embossed pattern corresponding to thedigital information signal is formed on the conductive film 134 using aphotoresist film 133, as shown in FIG. 13(b). The section profile of theprotruding portion formed with the photoresist film 133 is a trapezoidwith an upper side at the surface that is longer than a lower side onthe substrate as shown in FIG. 13(b).

[0141] Then, as shown in FIG. 13(c), a ferromagnetic film 132 is formedon the conductive film 134 and the protruding portion of the photoresistfilm 133 with an electroplating method.

[0142] Then, the photoresist film 133 is removed. Thus, as shown in FIG.13(d), the master information carrier is completed, which includes aconductive film 134 and a protruding portion of the ferromagnetic film132 whose section profile is a trapezoid with an upper side longer thana lower side. The photoresist film 133 is removed by melting thephotoresist film 133 by a solvent called “remover” in the same way asshown in FIG. 12(d).

[0143] Differently from the process shown in FIG. 12, this process shownin FIG. 13 forms the ferromagnetic film 132 by electroplating, so theferromagnetic material does not deposit on the surface of the protrudingportion of the photoresist film 133. Therefore, the photoresist film 133can be removed easier than in the process shown in FIG. 12. In addition,an etching step of the ferromagnetic film 132 is not required in thisprocess. The step for forming the conductive film 134, which is requiredin this process shown in FIG. 13, can be eliminated by using a substrate131 made of a conductive material.

[0144] Though the material and thickness of the conductive film 134 arenot limited, it is preferable to obtain a film with a smallsurface-roughness. If the surface-roughness of the conductive film 134is large, the surface-roughness of the ferromagnetic film 133 formedthereon may also become large, and the surface-roughness can influence adistribution of the magnetic field for preformat writing. Therefore, itis desirable to select the continuous thin film material with littlesurface roughness and as thin as possible, as long as a sufficientconductivity for electroplating can be obtained.

[0145] If the reflectivity of the surface of the conductive film 134 islarge at a wavelength region of light for exposing the photoresist film,the resolution at exposure can be deteriorated due to the influence ofthe reflecting light. Therefore, it is desirable to use a material forthe conductive film whose reflectivity at the surface is small,preferably less than 50% at a wavelength of light for exposing thephotoresist film 133.

[0146] As mentioned above, the resolution at exposing the photoresistfilm can be improved when the conductive film 134 has a function ofanti-reflection coating compared with the case where the patterning ofthe resist film is performed directly on the substrate 131. Thisconductive film 134 with anti-reflection function can be a conductivecarbon film or a film with some impurities containing a carbon as a maincomponent, for example.

[0147] It is also preferable when selecting a material for theconductive film to consider a compatibility of the material with theferromagnetic material to be disposed on the conductive film 134.Deposition rate, construction or magnetic characteristics of theferromagnetic film 132 formed on the conductive film by electroplatingmay change depending on the material of the conductive film. Therefore,it is preferable to select the most proper conductive film materialconsidering the ferromagnetic film material to be used.

[0148] If the substrate material is selected from conductive material,it is preferable to pay the same attention as mentioned above concerningthe conductive film.

[0149] In the example of the process for making a master informationcarrier having the second configuration mentioned above, the sectionprofile of the protruding portion of the photoresist film 133 ispermitted to be a trapezoid. Therefore, a regular, widely usedphotolithography process can be used without using a special advancedphotolithography technique. Thus, the master information carrier can beproduced efficiently at low cost in the same way as the masterinformation having the first configuration explained previously.

[0150] (Third Embodiment)

[0151] It is necessary that the surface of the master informationcarrier and the surface of the magnetic record medium keep a uniform andsecure contact when writing a master information into the magneticrecord medium. If secure and uniform contact is not kept between the twosurfaces, the master information signal can be written incorrectly intothe magnetic record medium due to spacing loss. In this case, the readsignal from the medium may include a partial lack of data ordeteriorated S/N ratio.

[0152] This embodiment provides a suitable configuration of the masterinformation carrier for maintaining a secure and uniform contact betweenthe surface of the master information carrier and the surface of themagnetic record medium, a master information carrier that can performpreformat writing with high reliability, as well as a method forproducing the master information carrier.

[0153] If the magnetic record medium into which the master informationis preformat-written is a hard disk, its substrate is a hard materialsuch as metal, glass, silicon or carbon. Therefore, it is preferablethat the substrate of the master information carrier has flexibility toa certain extent so that the surface of the master information carriercan compensate a fine wimple or bending to keep a secure contact stateover the whole disk surface. A polymer material is suitable for makingsuch a substrate of the master information carrier.

[0154] The master information carrier of the present invention can keepa secure and uniform contact with the surface of the hard disk thatincludes a hard substrate and a magnetic film formed on the substrate,by using a polymer material for the substrate of the master informationcarrier. Thus, the master information carrier of the present inventioncan raise the reliability of the preformat writing.

[0155] However, for preformat recordings of harddisks having a futureareal recording density in the 10-gigabit-order, substantial improvementwas found to be necessary in environmental resistance properties orhandling properties when using a polymer material that is soft comparedto the hard disk substrate for the substrate of the master informationcarrier. For example, dimension stability against an expansion orcontraction due to a change of temperature or humidity, a physical andchemical stability in the process for making the master informationcarrier, and a processability of the material should be raised. Inaddition, to ensure a secure and uniform contact between the surface ofthe master information carrier and the surface of the magnetic recordmedium, an electrostatic sticking of dust should be suppressed.

[0156] The inventors have studied the structure of master informationcarriers having a substrate that includes a polymer material. As aresult, it was found that the above mentioned problems are solved byusing a master information carrier having a structure as explainedbelow.

[0157] First, a structure for improving the environmental resistanceproperty is explained. A substantially high accuracy of dimensionsshould be required of the substrate of the master information carrier towrite preformat data into a hard disk having an areal recording densityof 10-giga-bit order in the future. Furthermore, this high accuracyshould be realized in various circumstances such as manufacturingprocess, preformat-writing step, and storing of the master informationcarrier. There is no material that can satisfy such a request for theenvironmental resistance by itself alone.

[0158] For example, polyimide and polyamide resins have excellentstability against heat and chemicals, but they have a tendency to expanddue to water absorption. The tendency of polyethylenetherephtalateresins to absorb water and expand is relatively small, but heatstability is a problem.

[0159] Polypropylene or Teflon (trademark of polytetrafluorethylene)resins have excellent stability of dimension under variouscircumstances, but they have weak adhesiveness with the ferromagneticfilm.

[0160] The substrate of the master information carrier according to thepresent invention has a multi-layer construction of at least two of thepolymer materials having different properties as mentioned above. Thus,the advantages of each material are utilized and disadvantages of eachmaterial are compensated.

[0161] As one of the preferable examples, the substrate of the masterinformation carrier has a multi-layer construction of a polypropylene orTeflon resin and a polyimide or a polyamide resin. This masterinformation carrier can maintain an excellent dimension stability undera variety of circumstances, owing to the properties of the polypropyleneor Teflon resin, while it has sufficient adhesiveness with theferromagnetic film that is formed on the surface of the polyimide orpolyamide resin.

[0162] The appropriate combination of polymer material and thickness ofeach layer for such a multi-layer construction can be changed dependingon the thermal history in the process for making the master informationcarrier, temperature and humidity when writing preformat data,temperature and humidity when storing the master information carrier andother conditions. It is necessary to select the most suitablecombination and thickness ratio of layers in accordance with eachcondition.

[0163] Second, a structure for improving the processability isexplained. It is sometimes necessary to process the master informationcarrier into a proper shape in accordance with a shape of the magneticrecord medium after forming the embossed pattern corresponding to themaster information. For example, the master information carrier that isused for writing preformat master information into a hard diskpreferably has a proper dimension corresponding to a certain diameter ofthe hard disk, so that it can be easily handled for preformat writing.

[0164] However, a master information carrier having a substrate made ofa polymer material usually has a bad processability. Especially, plasticor other deformation sometimes occurs in the process, and deteriorationof dimension accuracy may occur due to the deformation.

[0165] The master information carrier of the present invention has asubstrate including a base made of a metal, alloy or ceramic material;and a polymer material layer formed on the surface of the base. Theprocessability of the whole master information carrier is improved andplastic deformation hardly occurs in the polymer material layer formedon the surface of the base, resulting from the excellent processabilityof the relatively hard base. In addition, a macroscopic stability inshape and handling properties of the master information carrier areraised as a result of the excellent processability of the hard base.

[0166] It is difficult for the hard base to meet a fine wimple orbending of the magnetic record medium. However, the flexible polymermaterial layer formed on the surface of the substrate can compensate afine wimple or bending of the magnetic record medium to ensure secureand uniform contact state between the protruding portion of theferromagnetic film of the master information carrier and the surface ofthe magnetic record medium.

[0167] Furthermore, when the master information carrier comprises a basemade of a metal, alloy or ceramic material and a polymer material layerformed on the surface of the base, the effect of dimension accuracyconcerning environmental resistance can be improved, too.

[0168] The polymer material layer can be formed on the surface of thebase by a variety of methods such as sticking, coating or flowing ofmonomer or polymer precursor followed by polymerization after thecoating or flowing, or vacuum vapor deposition of the polymer material.

[0169]FIG. 14 illustrates an example of the process for making themaster information carrier having the above-mentioned structure.

[0170] First, a polyimide solution (Torayneece: trademark of TorayIndustry Inc.) is diluted with cyclohexanol into a predeterminedconcentration, and is coated onto the surface of the glass base 141 byusing a spin-coater. Then, it is cured at high temperature to obtain thesubstrate comprising the glass base 141 and the polyimide layer 142formed on the glass base 141, as shown in FIG. 14(a). The thickness ofthe polyimide layer 142 should be optimized depending on the conditionof the application. In one example, it was approximately 1.0 micronafter curing.

[0171] Then, a photoresist film 144 is formed on the polyimide layer142, and exposed and developed to make the embossed patterncorresponding to the master information signal as shown in FIG. 14(b).

[0172] Then, a ferromagnetic film 143 is formed on the polyimide layer142 and the protruding portion of the photoresist film 144 by usingvariety of methods such as a vacuum vapor deposition, sputtering, orplating.

[0173] Finally, the photoresist film 144 and the ferromagnetic film 143are removed by the liftoff method. As a result, the master informationcarrier is obtained as shown in FIG. 14(c), which comprises a substrateincluding the glass base 141 and the polyimide layer (polymer materiallayer) 142, and the protruding portion 143 of the ferromagnetic filmformed on the polyimide layer 142 of the substrate.

[0174] The polymer material layer can include a plurality of polymermaterials and is not limited to a single material, consideringelasticity, resistance to chemicals, or other properties. A developerfor developing the photoresist film, a remover for liftoff, an etchantfor wet etching and other solutions are usually strong acid or alkaline.The polymer material such as a polyimide or a polyamide has an excellentresistance to acid or alkali and is suitable for the material formingthe very surface of the substrate.

[0175] Next, a structure for preventing the master information carrierfrom gathering dusts by static electricity in the preformat writing stepis explained. The electrostatic sticking of dust during the preformatwriting step should be suppressed to ensure a secure and uniform contactof the surface of the master information carrier with the surface of themagnetic record disk. If dust sticks to a spot of the surface of themaster information carrier, a deterioration of the S/N ratio of the readsignal or partial lack of read signal may occur at the spot due tospacing loss.

[0176] In the master information carrier of the present invention, thepolymer material that forms at least the surface of the substrate has aconductivity that can prevent the substrate from taking an electriccharge. Thus, the electrostatic sticking of dust to the masterinformation carrier is suppressed and the preformat writing can beperformed with high reliability.

[0177] Particles whose main component is a conductive substance may bedispersed in the polymer material that forms at least the surface of thesubstrate. The main component of such particles is preferably a carbon.Such particles whose main component is a carbon can be dispersed easilyin the polymer material and are inexpensive.

[0178] As another example of the structure for preventing theelectrostatic sticking of a dust, a thin conductive film (e.g., a thinmetal film) may be formed on the surface of the polymer material layerformed on the surface of the base, wherein a thickness of the conductivefilm should be thin enough not to obstruct the elasticity of the polymermaterial layer. For example, in the process, the thin conductive film isformed on the surface of the base made of polymer, and the embossedpattern is formed with the ferromagnetic film on the conductive film.This construction can prevent electrostatic and sticking of dust sincethe surface of the master information carrier is made of only conductivematerial.

[0179] (Fourth Embodiment)

[0180] As mentioned above, it is necessary to ensure a secure anduniform contact between surfaces of the master information carrier andthe magnetic record medium in the writing process of the masterinformation for maximizing the effect of the writing method of thepresent invention. If the secure and uniform contact between thesurfaces is not obtained, a spacing loss causes a partial lack of a readsignal, or deterioration of S/N ratio due to a small written signallevel. In addition, the magnetic transition may not be sharp at theedges of a track due to diffusing of the magnetic field for writing, sothat sufficient off-track characteristics may not be obtained.

[0181] The master information carrier of this embodiment can ensure thesecure and uniform contact between the surface of the master informationcarrier and the surface of the magnetic record medium by a differentconfiguration from that of the third embodiment mentioned above. Asuitable apparatus for writing the master information into a magneticrecord medium with high reliability using this master informationcarrier is also provided.

[0182] A first configuration of the master information carrier of thisembodiment has a substrate surface including areas where an embossedpattern corresponding to information signal is formed and areas wherethe embossed pattern is not formed. A ferromagnetic film is formed atleast on surfaces of protruding portions of the embossed pattern, andthrough holes are provided at least partially in the area where theembossed pattern is not formed.

[0183] A second configuration of the master information carrier of thisembodiment comprises an area in a surface of a substrate, where anembossed pattern is formed corresponding to information signal, andanother area where the embossed pattern is not formed, wherein a heightof the surface of at least a part of the area where the embossed patternis not formed is lower than that of the area where the embossed patternis formed.

[0184] The apparatus for writing an information signal into a magneticrecord medium using the above-mentioned master information carriercomprises means for forcing the master information carrier and themagnetic record medium to contact with each other, means for positioningthe master information carrier and the magnetic record medium, and meansfor applying a magnetic field for exciting the ferromagnetic film formedon the surface of the protruding portion of the master informationcarrier.

[0185] A first concrete configuration of the apparatus mentioned aboveutilizes the master information carrier having through holes provided atleast partially in the area where the embossed pattern is not formed, asmentioned above as the first configuration. The apparatus has means toforce the master information carrier (embossed pattern) and the magneticrecord medium to contact securely with each other by sucking air betweenthe master information carrier and the magnetic record medium throughthe through holes after the master information carrier and the magneticrecording medium are contacted with each other.

[0186] A second specific configuration of the apparatus mentioned aboveutilizes the master information carrier whose height of the surface ofat least a part of the area where the embossed pattern is not formed islower than that of the area where the embossed pattern is formed, asmentioned above as the second configuration. The apparatus has means toforce the embossed pattern of the master information carrier and themagnetic record medium to contact securely with each other by suckingout air between the area of the master information carrier where theembossed pattern is not formed, and the magnetic record medium after themaster information carrier and the magnetic recording medium arecontacted with each other.

[0187] Using the above-mentioned master information carrier and writingapparatus, a magnetic record medium can contact with the masterinformation carrier securely and uniformly. Thus a preformat writing canbe performed with high reliability.

[0188] It is preferable that the apparatus comprises a pair of flangesas means to force the master information carrier and the magneticrecording medium to contact tightly with each other, between which themaster information carrier and the magnetic record medium are disposed,and members for fastening the periphery of the pair of flanges to eachother. If the above-mentioned means with the air suction mechanismfurther comprises these flanges and fastening members, a more secure anduniform contact can be obtained between the master information carrierand the magnetic record medium. When a duct for air suction is connectedto a center portion of the master information carrier or the magneticrecord medium, the suction force may be applied to the center portionstrongly, so that the master information carrier or the magnetic recordmedium may have a warp. In this case, the above mentioned flanges andfastening members suppress the warp so that the master informationcarrier and the magnetic record medium can contact securely anduniformly. It is more preferable to insert an elastic member between oneflange and the master information carrier, and/or, between the otherflange and the magnetic record medium. Thus, the master informationcarrier and the magnetic record medium can contact more securely anduniformly.

[0189] The above-mentioned means for alignment of the master informationcarrier and the magnetic recording medium preferably include a markerprovided at the inner circumference or outer circumference of the masterinformation carrier corresponding to the inner circumference or outercircumference of the magnetic record medium.

[0190] The following the configurations of this embodiment of thepresent invention in detail, referring to FIGS. 15-21.

[0191]FIG. 16 is a cross section showing an example of an apparatus forwriting information signal provided in the master information carrierinto a magnetic record medium. Numeral 161 a and 161 b denote masterinformation carriers, 162 denotes a hard disk, 163 denotes an upperflange, 164 denotes a lower flange, 165 a and 165 b denote permanentmagnets, 166 a and 166 b denote air suction devices, 167 a and 167 bdenote three-way valves, 168 a and 168 b denote suction ducts, and 160denotes an O-ring. The magnetization direction of the permanent magnets165 a, 165 b is from back to front of the paper.

[0192] The surface of the master information carrier 161 a, 161 bincludes an area 152 disposed once every predetermined angular distance,where a fine embossed pattern is formed corresponding to the informationsignal as shown e.g. in FIG. 15. Apart of the area 152 (region B in FIG.15) is shown enlarged in FIG. 1. As explained in the first embodiment,the master information provided as an embossed pattern in area 152includes a tracking servo signal, a clock signal and address informationsignal that are disposed sequentially along the track direction. In FIG.1, the hatched portions are protruding portions whose surface is made ofa ferromagnetic material such as Co or Ni—Fe.

[0193] As mentioned in the first embodiment, a preferable step heightbetween the surface of the protruding potion and the bottom of theembossed pattern corresponding to the information signal variesdepending on surface properties of the magnetic record medium into whichthe master information is written and the bit size of the masterinformation. In general, it is more than 0.05 micron, preferably morethan 0.1 micron. It was 0.5 micron in one example.

[0194] As shown in FIG. 15, the master information carrier 151 hasthrough holes 153 except at areas 152 where the embossed pattern isformed corresponding to the information signal. If the substrate of themaster information carrier is made of glass, the through holes 153 canbe formed by well-known processes such as an ultrasonic process, a laserprocess or wet etching and other methods. It is preferable that adiameter of the through holes is as small as possible and the number ofthe through holes is as large as possible. In an example, through holeswith a diameter of 1.0 mm were disposed in a density of 1.0 per 3.0mm×3.0 mm area by ultrasonic processing.

[0195] When writing the master information signal into a hard disk, i.e.a magnetic record medium, centering of the master information patternand the hard disk is required before contacting them. To facilitate thiscentering, the master information carrier 151 has markers 154 at theinner circumference as shown in FIG. 15. The marks are formed in samethe step in which the embossed pattern corresponding to the informationsignal is formed. The markers 154 disposed at the inner circumference ofthe master information carrier 151 are aligned to the innercircumference of the hard disk. Alternatively, markers can be disposedat the outer circumference of the master information carrier 151 to bealigned to the outer circumference of the hard disk. If the magneticrecord medium is not a disk having an inner circumference, but amagnetic card or other sheet medium, markers of the master informationcarrier 151 disposed at the outer circumference of the magneticrecording medium may work for alignment. Thus, a position, shape ornumber of the marker should be optimized in accordance with aconfiguration of the magnetic record medium.

[0196]FIG. 17 shows a method for writing the information signal formedon the master information carrier into a hard disk using the writingapparatus shown in FIG. 16. The writing apparatus shown in FIG. 16utilizes an atmospheric pressure for ensuring a uniform contact in thewhole area between the master information carriers 161 a, 161 b and thehard disk 162. The hard disk is forced to the master information carrier161 a, 161 b when air between the master information carrier 161 a, 161b and the hard disk 162 is sucked out via the through holes that areprovided in the master information carrier 161 a, 161 b. Thus, thesurface of the protruding portion of the embossed pattern formed on themaster information carrier 161 a, 161 b contacts securely with thesurface of the hard disk 162. Then, utilizing the permanent magnets 165a and 165 b, the ferromagnetic film, formed on the surface of theprotruding portion of the embossed pattern formed on the masterinformation carrier 161 a and 161 b, is magnetized to write theinformation signal corresponding to the embossed pattern into the harddisk 162, according to the steps explained below.

[0197] First, by using a permanent magnet 182, the hard disk 162 ispreviously magnetized along the circumferential direction indicated byarrow 181 as shown in FIG. 18. The permanent magnet 182 can be replacedwith an electromagnet. Then, as shown in FIG. 16, an O-ring 160 is setin the groove of the lower flange 164, on which the master informationcarrier 161 b and the hard disk 162 are stacked on the hard disk 162. Atthis time, the previously mentioned markers (154 in FIG. 15) formed onthe master information carrier 161 b should be aligned to the innercircumference of the hard disk 162. Then, another master informationcarrier 161 a and the upper flange 163 with an O-ring 160 set in thegroove are stacked on the hard disk 162. At this time too, markersformed on the master information carrier 161 a should be aligned to theinner circumference of the hard disk 162.

[0198] Operating the upper three-way valve 167 a, air between the upperflange 163 and the master information carrier 161 a is sucked out by theair suction device 166 a. At this time, the lower three-way valve 167 bshould be opened so that atmospheric pressure exists in the spacebetween the lower flange 164 and the master information carrier 161 b.When air between the master information carrier 161 a and the hard disk162 is sucked out via through holes 169 provided to the masterinformation carrier 161 a, the hard disk 162 is pressed to the masterinformation carrier 161 a and they are contacted securely with eachother. Then, as shown in FIG. 17(a), the permanent magnet 165 a is movedaround the suction duct 168 a and in parallel to the surface of theupper flange 163 to apply a direct exciting field 171 a. Thus, theferromagnetic film of the protruding portion formed on the masterinformation carrier 161 a is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 162. The harddisk 162 is previously magnetized along the direction of thecircumference by using the permanent magnet as mentioned above. Thepolarity of this initial magnetization and the polarity of magneticfield applied by the permanent magnet 165 a for writing informationsignal are usually opposite. However, as mentioned in the firstembodiment, it may be preferable that they are the same polarity in somecases. Therefore, the suitable polarity should be selected to achieve afavorable S/N ratio. In an example, they were opposite.

[0199] Next, operating the lower three-way valve 167 b, air between thelower flange 164 and the master information carrier 161 b is sucked outby the air suction device 166 b. At this time, the upper three-way valve167 a should be opened so that atmospheric pressure exists in the spacebetween the upper flange 163 and the master information carrier 161 a.When air between the master information carrier 161 b and the hard disk162 is sucked out via through holes 169 formed in the master informationcarrier 161 b, the hard disk 162 is pressed to the master informationcarrier 161 b and they are contacted securely with each other.

[0200] As shown in FIG. 17(b), the permanent magnet 165 b is movedaround the suction duct 168 b and in parallel to the surface of thelower flange 164 to apply a direct exciting field 171 b. Thus, theferromagnetic film of the protruding portion formed on the masterinformation carrier 161 b is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 162. In anexample, the polarity of the initial magnetization applied to the harddisk 162 and the polarity of magnetic field applied by the permanentmagnet 165 b for writing information signal were opposite.

[0201] As explained above, preformat data is written into both sides ofthe hard disk 162 in a short time. An electromagnet can be used insteadof the permanent magnet to magnetize the ferromagnetic film of theprotruding portion formed on the master information carrier. It isdesirable that the material of the upper and lower flanges 163, 164,between the permanent magnet and the master information carrier is anonmagnetic material such as a brass, so that the ferromagnetic film onthe surface of the master information carrier can be magnetized.

[0202] If the magnetic record medium is not a hard disk but a flexibledisk in the configuration shown in FIG. 16, and if the through holesformed in the master information carrier are large, the flexible diskmay be sucked partially into the through holes and deformed, resultingin failure of preformat writing into correct positions or in lack ofsignal to be written. Therefore, as mentioned before, it is preferableto provide as many small through holes as possible. Thus, this apparatuscan write the preformat signal not only into a hard disk but also into aflexible disk with high reliability. The apparatus shown in FIG. 16comprises a pair of master information carriers 161 a and 161 b disposedat both sides of the magnetic record medium, so the preformat writingcan be performed efficiently in a short time for both sides of themagnetic record medium. Thus, productivity is further improved.

[0203]FIG. 20 is a cross section showing another example of theapparatus for writing information signal provided in the masterinformation carrier into a magnetic record medium. Numeral 201 denotes amaster information carrier, 202 denotes a hard disk, 203 denotes anupper flange, 204 denotes a lower flange, 205 denotes a permanentmagnet, 200 a and 200 b denote elastic plates, 206 denotes an airsuction device, 207 denotes a three-way valve, 208 denotes a suctionduct, and 209 denotes bolts for fastening the upper flange 203 and thelower flange 204.

[0204] The surface of the master information carrier 201 includes anarea 192 disposed once every predetermined angular distance where a fineembossed pattern is formed corresponding to the information signal asshown in FIG. 19(a). Similarly to the configuration shown in FIG. 15, anexample of enlarged pattern of this area 192 is shown in FIG. 1.

[0205] In the master information carrier 191 shown in FIG. 19(a),compared with the areas 192 where the embossed pattern is formed and aperipheral area 191 (non-hatched area in FIG. 19(a)), the other area 193(hatched area in FIG. 19(a)) has lower height of the surface. This area193 is called “lowered area” hereinafter. FIG. 19(b) shows a surfacecontour of a section of FIG. 19(a) along the phantom curve line C-C′. Onthe surface of the area 192, the embossed pattern is formedcorresponding to the information signal as shown in FIG. 1. Afterforming the embossed pattern by photolithography or other method, thelowered area 193 is formed by using a well-known method such asmachining, supersonic process or laser process. The height differencebetween the area 192 where the embossed pattern is formed and thelowered area 193 is preferably more than 10 micron, more preferably morethan 100 micron, though it depends on the thickness of the substrate ofthe master information carrier 191.

[0206] When writing the information signal formed on the masterinformation carrier into a hard disk, i.e. a magnetic record medium,centering of the master information pattern and the hard disk isrequired before contacting them. As shown in FIG. 19(a), the masterinformation carrier 191 has markers 194 at the inner circumference. Themarkers 194 are aligned to the inner circumference of the hard disk.Alternatively, markers can be disposed at the outer circumference of themaster information carrier 191 to be aligned to the outer circumferenceof the hard disk.

[0207]FIG. 21 shows a method for writing the master information formedon the master information carrier into a hard disk by using the writingapparatus shown in FIG. 20. The writing apparatus shown in FIG. 20ensures a uniform contact between the master information carrier 201 andthe hard disk 202 not only by utilizing an atmospheric pressure but alsomechanically. There are spaces between the hard disk 202 and the loweredareas 193 of the master information carrier 201. Air in the spaces issucked out for ensuring the secure contact between the hard disk and thearea of the master information carrier where the embossed pattern isformed corresponding to the information signal. Then, utilizing thepermanent magnet 205, the ferromagnetic film, formed on the surface ofthe protruding portion of the embossed pattern formed on the masterinformation carrier 201 is magnetized to write the information signalcorresponding to the embossed pattern into the hard disk 202 accordingto the steps explained below.

[0208] First, as shown in FIG. 18, by using a permanent magnet 182, thehard disk 202 is previously magnetized in the circumferential directionindicated by arrow 181. Then, as shown in FIG. 20, the elastic plate 200b, the hard disk 202 and the master information carrier 201 are stackedin turn on the lower flange 204. The elastic plate 200 b has a throughhole at the center, whose diameter is substantially the same as a centerhole of the hard disk 202. At this time, the previously mentionedmarkers (194 in FIG. 19) should be aligned to the inner circumference ofthe hard disk 202. Then, another elastic plate 200 a and upper flange203 are stacked on the master information carrier 201. The elasticplates 200 a and 200 b can be made of a variety of materials such as asilicone rubber.

[0209] Operating the three-way valve 207, air between the lowered area193 of the master information carrier 201 and the hard disk 202 issucked out by the air suction device 206. As a result, the hard disk 202and the area of the master information carrier where the embossedpattern is formed contact securely with each other. The suction duct 208is disposed at the center of the apparatus as shown in FIG. 20, so anexhaust conductance is large at the center portion of the masterinformation carrier 201. Therefore, the air suction effect is strong atthe center portion but weak at the peripheral portion of the masterinformation carrier 201. Consequently, it is possible that a securecontact between the hard disk 202 and the master information carrier 201is not obtained at the peripheral portion.

[0210] To solve this problem, elastic plates 200 a and 200 b aredisposed between the upper flange 203 and the master information carrier201 as well as between the lower flange 204 and the hard disk 202, andin addition, the peripheral portions of the upper and lower flanges 203,204 are fastened to each other with bolts 209, as shown in FIG. 20.Adjusting the fastening force of each bolt 209, the hard disk 202 andthe master information carrier 201 are contact with each other securelyand uniformly. Thus, the hard disk 202 and the area of the masterinformation carrier 201 where the embossed pattern is formedcorresponding to the information signal are contact with each otheruniformly over a whole surface.

[0211] Finally, as shown in FIG. 21, a direct exciting field 211 isapplied by moving the permanent magnet 205 along circumferentialdirection and in parallel to the surface of the upper flange 203. Bythis operation, the ferromagnetic film of the protruding portion of theembossed pattern corresponding to the information signal is magnetizedand the information signal is written into the hard disk 202. The harddisk 202 is previously magnetized along the circumferential direction byusing the permanent magnet. The polarity of this initial magnetizationand the polarity of magnetic field applied by the permanent magnet 205are usually opposite. However, in some cases, the same polarity betweenthem is preferable depending on the embossed pattern formed on themaster information carrier. Therefore, the suitable polarity should beselected for good S/N ratio of the read signal according to eachcondition of application. In one example, they were opposite.

[0212] It is desirable that a material of the upper flange 203 is anonmagnetic material such as a brass since the upper flange 203 isplaced between the permanent magnet 205 and the master informationcarrier 201.

[0213] As mentioned above, the configuration shown in FIG. 20 can obtaina more reliable preformat writing by sucking out the air between thehard disk and the lowered area of the master information carrier, and byfastening the peripheral portion of them with the bolts.

[0214] The present invention, though explained with several examples,can be utilized in a variety of embodiments. For example, theapplications of the present invention are not limited to preformatwriting of a magnetic disk, but include preformat writing of a magneticcard, magnetic tape, or other magnetic record medium.

[0215] The present invention can be applied to writing informationsignals into a magneto-optical record medium or other magnetic recordmedia that use a variety of optical effects for reproducing the signal.When writing information signal into a magneto-optical record medium byusing the method of the present invention, the magneto-optical recordmedium may be heated to the Curie temperature or near the compensationtemperature to perform writing under the condition where the spontaneousmagnetization is vanished. This method is called a “thermo-magneticwriting method” and is advantageous.

[0216] Furthermore, the information signal to be written into themagnetic record medium is not limited to the preformat data such as atracking servo signal, address, clock and other signals. It is possibleto apply the present invention to writing a variety of data, audio,video or other signals. In these applications, mass production ofsoftware can be performed by utilizing the present invention to providesoftware at low cost.

1. A master information carrier for writing an information signal into amagnetic record medium, comprising an embossed pattern corresponding tothe information signal formed on a substrate, and a ferromagneticmaterial that forms at least a surface of a protruding portion of theembossed pattern.
 2. The master information carrier according to claim1, wherein the ferromagnetic material is a soft magnetic material. 3.The master information carrier according to claim 1, wherein theferromagnetic material is a hard or semihard magnetic material witheither a coercive force in the inplane direction or a coercive forceperpendicular to the substrate that is not more than 40 kA/m.
 4. Themaster information carrier according to claim 1, wherein theferromagnetic material has a saturation magnetic flux density of atleast 0.8 T.
 5. The master information carrier according to claim 1,wherein at least a part of the substrate has flexibility.
 6. The masterinformation carrier according to claim 5, wherein the substratecomprises a polymer material.
 7. The master information carrieraccording to claim 6, wherein the substrate has a multi-layerconstruction including plural kinds of polymer material.
 8. The masterinformation carrier according to claim 6, wherein the polymer materialof the substrate has electrical conductivity.
 9. The master informationcarrier according to claim 6, wherein particles mainly composed ofconductive substance are dispersed in the polymer material of thesubstrate.
 10. The master information carrier according to claim 9,wherein the conductive substance is mainly composed of carbon.
 11. Themaster information carrier according to claim 6, wherein a conductivethin film is formed on the substrate comprising a polymer material, anembossed pattern corresponding to the information signal is formed onthe conductive thin film, and at least the protruding portion of theembossed pattern is composed of a ferromagnetic material.
 12. The masterinformation carrier according to claim 5, wherein the substratecomprises a base made of metal, alloy or ceramic material and a layer ofa polymer material formed on the base.
 13. The master informationcarrier according to claim 12, wherein the substrate comprises a polymerfilm applied to the surface of the base.
 14. The master informationcarrier according to claim 12, wherein the substrate comprises a polymerlayer formed by polymerization after coating or flowing of monomer orprecursor of polymer on the surface of the base.
 15. The masterinformation carrier according to claim 12, wherein the polymer layer isformed by vacuum vapor deposition on the surface of the base.
 16. Themaster information carrier according to claim 12, wherein the surfacelayer formed on the surface of the base has a multi-layer structure madeof plural kinds of polymer material.
 17. The master information carrieraccording to claim 12, wherein the polymer material on the surface ofthe base has electrical conductivity.
 18. The master information carrieraccording to claim 12, wherein particles which are mainly composed of aconductive substance are dispersed in the polymer material on thesurface of the substrate.
 19. The master information carrier accordingto claim 18, wherein the conductive substance is mainly composed ofcarbon.
 20. The master information carrier according to claim 12,wherein a conductive thin film is formed on a substrate surface composedof the polymer material, an embossed pattern corresponding to theinformation signal is formed on the conductive thin film, and at leastthe protruding portion of the embossed pattern is composed of aferromagnetic material.
 21. A master information carrier for writing aninformation signal into a magnetic record medium, comprising a substratethat is composed of a ferromagnetic material and an embossed patterncorresponding to the information signal, which is formed on the surfaceof the substrate.
 22. The master information carrier according to claim21, wherein the ferromagnetic material forming the substrate is a softmagnetic material.
 23. The master information carrier according to claim21, wherein the ferromagnetic material forming the substrate is a hardor semihard magnetic material with either a coercive force in theinplane direction or a coercive force perpendicular to the substratethat is not more than 40 kA/m.
 24. The master information carrieraccording to claim 21, wherein the ferromagnetic material has asaturation magnetic flux density of at least 0.8 T.
 25. The masterinformation carrier according to claim 1, wherein an embossed patterncorresponding to a digital information signal is formed on the surfaceof the substrate, the ferromagnetic material is formed at least at theprotruding portion of the embossed pattern, the cross section of theprotruding portion along bit length direction of the digital informationsignal has a substantially trapezoidal shape with an upper side at thesurface that is shorter than a lower side on the substrate, and a lengthdifference between the upper and lower sides is not more than twice theheight of the trapezoid.
 26. The master information carrier according toclaim 25, wherein curvature radii at edges of the upper side of thetrapezoid are not more than a half of the upper side length.
 27. Themaster information carrier according to claim 25, wherein a thickness ofthe ferromagnetic material layer at the protruding portion is not morethan a half of the upper side length, so that the master informationcarrier is suitable for writing information into an in-plane magneticrecord medium.
 28. The master information carrier according to claim 25,wherein a thickness of the ferromagnetic material layer at theprotruding portion is more than twice of the upper side length, so thatthe master information carrier is suitable for writing information intoa perpendicular magnetic record medium.
 29. The master informationcarrier according to claim 1, wherein an embossed pattern correspondingto a digital information signal is formed on the surface of thesubstrate, the ferromagnetic material is formed at least at theprotruding portion of the embossed pattern, the cross section of theprotruding portion along bit length direction of the digital informationsignal has a substantially trapezoidal shape with an upper side at thesurface that is longer than a lower side on the substrate.
 30. Themaster information carrier according to claim 29, wherein a thickness ofthe ferromagnetic material layer at the protruding portion is not morethan a half of the upper side length, so that the master informationcarrier is suitable for writing information into an in-plane magneticrecord medium.
 31. The master information carrier according to claim 29,wherein a thickness of the ferromagnetic material layer at theprotruding portion is more than twice of the upper side length, so thatthe master information carrier is suitable for writing information intoa perpendicular magnetic record medium.
 32. The master informationcarrier according to claim 1, wherein the surface of the substratecomprises areas where the embossed pattern corresponding to aninformation signal is formed and areas where the embossed pattern is notformed, the ferromagnetic material is provided at least at the surfaceof the protruding portion of the embossed pattern, and through holes areprovided at least partially in the area where the embossed pattern isnot formed.
 33. The master information carrier according to claim 1,wherein the surface of the substrate comprises areas where the embossedpattern corresponding to an information signal is formed and areas wherethe embossed pattern is not formed, the ferromagnetic material isprovided at least at surfaces of protruding portions of the embossedpattern, and the surface height of at least a part of the areas wherethe embossed pattern is not formed is lower than the area where theembossed pattern is formed.
 34. A method for making a master informationcarrier that is used for writing an information signal into a magneticrecord medium, the method comprising the steps of: forming an embossedpattern corresponding to the information signal on a surface of asubstrate by using a photoresist film; forming a ferromagnetic thin filmon the embossed pattern; etching a surface of the ferromagnetic film;and removing the photoresist film and the ferromagnetic film on thephotoresist film by a liftoff method.
 35. The method according to claim34, wherein, in the step of forming an embossed pattern with aphotoresist film, a cross section of a protruding portion is formed intoa substantially trapezoidal shape with an upper side at the surface thatis shorter than a lower side on the substrate along the bit length of adigital information signal.
 36. The method according to claim 34,wherein the step of etching a surface of the ferromagnetic film isperformed by sputter etching or ion milling.
 37. The method according toclaim 36, wherein the incident angle of ions irradiated onto thesubstrate with respect to the normal of the substrate is at least 20degrees.
 38. The method according to claim 34, wherein the step ofetching a surface of the ferromagnetic film is performed with chemicaletching.
 39. A method for making a master information carrier that isused for writing an information signal into a magnetic record medium,the method comprising the steps of: forming a conductive thin film on asurface of a substrate; forming an embossed pattern corresponding to thedigital information signal on the conductive thin film with aphotoresist film; forming a ferromagnetic thin film on the conductivethin film forming the embossed pattern by using an electroplatingmethod; and removing the photoresist film.
 40. The method according toclaim 39, wherein a cross section of a protruding portion of theembossed pattern formed by the photoresist film has a substantiallytrapezoidal shape along the bit length of a digital information signalwith an upper side at the surface that is shorter than a lower side onthe substrate.
 41. The method according to claim 39, wherein areflectivity of the surface of the conductive thin film is not more than50% at the wavelength of the light source for exposing the photoresistfilm.
 42. The method according to claim 41, wherein the conductive thinfilm is mainly composed of carbon.
 43. A method for making a masterinformation carrier that is used for writing an information signal intoa magnetic record medium, the method comprising the steps of: forming anembossed pattern corresponding to a digital information signal on asurface of a conductive substrate by using a photoresist film; forming aferromagnetic thin film on the conductive substrate surface having theembossed pattern with an electroplating method; and removing thephotoresist film.
 44. The method according to claim 43, wherein, in thestep of forming an embossed pattern with a photoresist film, a crosssection of a protruding portion is formed into a substantiallytrapezoidal shape with an upper side at the surface that is shorter thana lower side on the substrate along the bit length of a digitalinformation signal.
 45. The method according to claim 43, wherein areflectivity of the surface of the conductive substrate is not more than50% at the wavelength of the light source for exposing the photoresistfilm.
 46. The method according to claim 45, wherein the conductivesubstrate is mainly composed of carbon.
 47. A method for writing aninformation signal into a magnetic record medium using a masterinformation carrier, the method comprising the steps of: preparing amaster information carrier whose surface has an embossed patterncorresponding to the information signal and at least a surface of theprotruding portion of the embossed pattern is made of a ferromagneticmaterial; and putting a surface of a sheet-shaped or disk-shapedmagnetic record medium having a ferromagnetic film or a ferromagneticcoating into contact with the surface of the master information carrierso as to write a magnetization pattern corresponding to the embossedpattern into the magnetic record medium.
 48. The writing methodaccording to claim 47, wherein the step of putting the surface of themagnetic record medium into contact with the surface of the masterinformation carrier includes application of an alternating bias magneticfield.
 49. The writing method according to claim 47, wherein the step ofputting the surface of the magnetic record medium into contact with thesurface of the master information carrier includes application of adirect exciting field for magnetizing the ferromagnetic material thatforms the surface of the protruding portion of the master informationcarrier.
 50. The writing method according to claim 47, wherein the stepof putting the surface of the magnetic record medium into contact withthe surface of the master information carrier includes application of analternating bias magnetic field and application of a direct excitingfield for magnetizing the ferromagnetic material that forms the surfaceof the protruding portion of the master information carrier.
 51. Thewriting method according to claim 47, wherein the step of putting thesurface of the magnetic record medium into contact with the surface ofthe master information carrier includes heating the magnetic recordmedium.
 52. The writing method according to claim 47, further comprisingthe step of erasing the magnetic record medium with a direct excitingfield before the step of putting the surface of the magnetic recordmedium into contact with the surface of the master information carrier.53. The writing method according to claim 47, wherein the ferromagneticmaterial that forms the protruding portion of the master informationcarrier is a soft magnetic material.
 54. The writing method according toclaim 47, wherein the ferromagnetic material that forms the protrudingportion of the master information carrier comprises a hard or semihardmagnetic material whose coercive force is not more than 40 kA/m in theinplane direction or perpendicular to the substrate.
 55. The writingmethod according to claim 47, wherein the ferromagnetic material thatforms the surface of the protruding portion of the master informationcarrier has a saturation magnetic flux density more than 0.8 T.
 56. Anapparatus for writing an information signal into a magnetic recordmedium with a ferromagnetic layer using a master information carrierthat comprises an embossed pattern corresponding to the informationsignal and a ferromagnetic material that forms at least the surface of aprotruding portion of the embossed pattern, the apparatus comprising:means for putting the magnetic record medium into contact with themaster information carrier; means for positioning the magnetic recordmedium and the master information carrier; and means for applying anexciting field to magnetize the ferromagnetic material that forms thesurface of the protruding portion of the master information carrier. 57.The apparatus according to claim 56, using a master information carrierwhose surface has an area with an embossed pattern corresponding to theinformation signal and an area without the embossed pattern, wherein themaster information carrier has through holes at least in the areawithout the embossed pattern, the means for putting the magnetic recordmedium into contact with the master information carrier sucking out airbetween the magnetic record medium and the master information carrierthrough the through holes in the master information carrier when themaster information carrier is in contact with the magnetic recordingmedium, so as to ensure secure contact between the magnetic recordmedium and the embossed pattern of the master information carrier. 58.The apparatus according to claim 56, using a master information carrierwhose surface has an area with an embossed pattern corresponding to theinformation signal and an area without the embossed pattern, wherein atleast a part of the area without the embossed pattern of the masterinformation carrier has a lower surface than the surface of the areawith the embossed pattern, the means for putting the magnetic recordmedium into contact with the master information carrier sucking out airbetween the magnetic record medium and the area without the embossedpattern of the master information carrier when the master informationcarrier is in contact with the magnetic recording medium, so as toensure secure contact between the magnetic record medium and theembossed pattern of the master information carrier.
 59. The apparatusaccording to claim 56, wherein the means for putting the magnetic recordmedium into contact with the master information carrier comprises a pairof flanges between which the magnetic record medium and the masterinformation carrier are disposed, and means for fastening peripheralportions of the flanges to each other.
 60. The apparatus according toclaim 59, further comprising an elastic material disposed either betweenone flange and the magnetic record medium or between the other flangeand the master information carrier or between both flanges and themagnetic recording medium and the master information carrierrespectively.
 61. The apparatus according to claim 56, wherein the meansfor positioning the magnetic record medium and the master informationcarrier are markers, which are disposed at an inner circumferenceportion of the master information carrier and aligned to an innercircumference portion of the magnetic record medium.
 62. The apparatusaccording to claim 56, wherein the means for positioning the magneticrecord medium and the master information carrier are markers, which aredisposed at an outer circumference portion of the master informationcarrier and aligned to an outer circumference portion of the magneticrecord medium.